1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display used in a display section of an information apparatus, a liquid crystal display having the same, and a method of manufacturing the same.
2. Description of the Related Art
Methods of mounting driver ICs (semiconductor chips) used for operating a liquid crystal display include COG (chip on glass) mounting, TAB (tape automated bonding) mounting, and COF (chip on film) mounting. COG satisfies recent needs for liquid crystal displays with thinner frames because it allows driver ICs for outputting video signals and control signals required for image display to be directly mounted on a glass substrate. Terminals at a signal output end of driver ICs are respectively connected to a plurality of terminal sections through bumps, the terminal sections being connected to a plurality of gate bus lines and drain bus lines extending from a display area. Terminals at a signal input end of the driver ICs are connected to terminal sections through bumps, the terminal sections being connected to FPCs (flexible printed circuits) that are provided separately. Some of the terminals at the signal input end are cascade-connected through in-panel wirings that are formed on a glass substrate.
Common wirings are provided in a liquid crystal display to keep the bus lines at the same potential in order to prevent thin film transistor (TFT) devices from being broken by static electricity generated at manufacturing steps. The common wirings are electrically connected to the bus lines and are provided at ends of a glass substrate.
FIG. 7 is a flow chart showing some of steps for manufacturing a liquid crystal display. First, alignment films are applied to surfaces (opposite surfaces) of a TFT substrate and an opposite substrate that have been fabricated at respective processes (step S1). Next, a rubbing process is performed on the alignment films on both of the substrates as occasions demand (step S2). Then, spacers having a spherical configuration, for example, are dispersed on either substrate (step S3). A sealing material is then applied to the periphery of each of panel forming areas on the other substrate, and the two substrates are combined to fabricate a combined substrate (step S4). Next, each of the two substrates is cut into a predetermined configuration to divide the combined substrate into individual panels (step S5). A liquid crystal is then introduced into and sealed a gap between the combined substrates thus divided to fabricate liquid crystal display panels (step S6).
The liquid crystal panels are then cleaned to remove any portion of the liquid crystal that has stuck to the surface of the liquid crystal display panels, and the panels are dried thereafter (step S7). Next, edges of each substrate are polished to chamfer them in order to prevent cracking and breakage at cut surfaces of the glass substrates (step S8). A polarizer is then applied to each of outer surfaces of the liquid crystal panels (step S9). The polarizers are provided such that their polarization axes are substantially orthogonal to each other. A display inspection is then conducted on the liquid crystal display panels (step S10). Driver ICs are then mounted on a surface of the TFT substrate (step S11). Liquid crystal displays are completed through the above-described steps.
The bus lines must be electrically isolated before the inspection step (step S10) in order to cause the liquid crystal displays to operate properly by inputting predetermined signals to each of the bus lines. Normally, the bus lines are electrically isolated by removing the common wirings at the panel dividing step (step S5) or the chamfering step (step S8). Alternatively, the bus lines are electrically isolated by irradiating the portions where the common wirings and the bus lines are connected with laser light to disconnect them prior to the inspection step.
FIG. 8 shows a configuration of a liquid crystal display according to the related art. As shown in FIG. 8, the liquid crystal display has a TFT substrate 102 and an opposite substrate 104 that are combined together through a sealing member (not shown) applied to the peripheries thereof. The TFT substrate 102 is formed with a plurality of gate bus lines 112 extending in the horizontal direction of the figure and a plurality of drain bus lines 114 extending in the vertical direction of the figure such that they intersect the gate bus lines 112 with an insulation film that is not shown interposed therebetween. Driver IC mounting areas 118 in which a plurality of driver ICs are mounted on a COG basis are provided at the left end of the TFT substrate 102. Terminal sections 116 provided in the driver IC mounting areas 118 are formed at the left ends of the respective gate bus lines 112.
Driver IC mounting areas 124 in which a plurality of driver ICs are mounted on a COG basis are provided at the bottom end of the TFT substrate 102. Terminal sections 122 provided in the driver IC mounting areas 124 are formed at the bottom ends of the respective drain bus lines 114.
FIG. 8 shows common wirings 120 and 126 that have already been removed at the panel dividing step (step S5). The common wiring 120 is provided at the right side of the TFT substrate 102 in the figure and is electrically connected to the gate bus lines 112. The common wiring 126 is provided at the top side of the TFT substrate 102 in the figure and is electrically connected to the drain bus lines 114. Although not shown, the common wiring 120 and the common wiring 126 are electrically connected to each other through a contact hole that is formed by providing an opening in the insulation film, for example.
FPC fitting areas 130 for inputting external signals are formed at the bottom of the driver IC mounting area 124 in the figure. The FPC fitting areas 130 are formed with terminal sections 132 and 133 that are connected to terminals at FPCs. The terminal sections 133 are electrically connected to terminal sections 123 of the driver IC mounting areas 124. The terminal sections 132 are electrically connected to terminal sections 117 of the driver IC mounting area 118 through an in-panel wiring 141. A terminal section 117 of the upper driver IC mounting area 118 in the figure is connected to a terminal section 117′ of the lower driver IC mounting area 118 in the figure through an in-panel wiring 140. Thus, a plurality of driver ICs mounted in the driver IC mounting areas 118 are cascade-connected.
The TFT substrate 102 and the opposite substrate 104 are offset at the ends thereof where the driver IC mounting areas 118 and 124 are located to provide a configuration in which a device forming surface of the TFT substrate 102 is exposed.
FIG. 9 shows another configuration of a liquid crystal display according to the related art. As shown in FIG. 9, a common wiring 121 electrically connected to gate bus lines 112 is formed at a side of a TFT substrate 102 where driver IC mounting areas 118 are located. A common wiring 127 electrically connected to drain bus lines 114 is formed at a side of the TFT substrate 102 where driver IC mounting areas 124 are located. Therefore, the inspection step (step S10) must be preceded by operations of irradiating a cutting line α with laser light to cut portions where the gate bus lines 112 and the common wiring 121 are connected and irradiating a cutting line β with laser light to cut portions where the drain bus lines 114 and the common wiring 127 are connected to isolate each of the gate bus lines 112 and each of the drain bus lines 114 electrically.
In the configuration shown in FIG. 8, however, since the common wirings 120 and 126 are disconnected at the panel dividing step (step S5) to electrically isolate the gate bus lines 112 and the drain bus lines 114 from each other, a problem arises in that the TFT devices can be broken by static electricity generated at subsequent steps (e.g., the liquid crystal introducing step (step S6)).
In order to solve this problem, a configuration may be employed in which the common wirings 120 and 126 are provided in regions that are located inside the dividing positions at the panel dividing step and that are removed at the chamfering step (step S8). However, in order to remove the common wirings 120 and 126 at the chamfering step, the TFT substrate 102 and the opposite substrate 104 must be offset also at the ends thereof where the common wirings 120 and 126 are provided to expose the surfaces of the TFT substrate 102 where the common wirings 120 and 126 are formed. This results in a problem in that the size of the TFT substrate 102 is increased to increase the surface area of a frame region of a liquid crystal display.
The configuration shown in FIG. 9 results in a problem in that there is an increase in steps of manufacturing liquid crystal displays because it involves an additional cutting step for electrically isolating the bus lines 112 and 114 by irradiating them with laser light. Another problem arises in that metals that are melt and spread during irradiation with laser light can cause connection defects when driver ICs are mounted.
FIG. 10 shows still another configuration of a liquid crystal display according to the related art. A relatively small number of signals are input to driver ICs at gate bus lines 112 from the outside, and there are a relatively small number of wirings (e.g., a few wirings) that are connected to the same from the outside. Therefore, as shown in FIG. 10, terminal sections 117 in driver IC mounting areas 118 for the gate bus lines 112 can be provided on shorter sides of the driver IC mounting areas 118 (on sides C in FIG. 10). Since this allows the gate bus lines 112 to be extended to the left end of the TFT substrate 102, a common wiring 121 can be provided in a location that is removed at the chamfering step (step S8). It is therefore possible to prevent static damage to TFT devices up to the chamfering step.
However, in the case of a liquid crystal display in which a great number of signals are input to driver ICs at gate bus lines 112 thereof and to which a great number of wirings are connected, shorter sides of driver IC mounting areas 118 have a great width. This results in a problem in that it is difficult to provide a liquid crystal display with a thin frame.